It is known to fasten a valve for controlling the flow of fuel to a structural panel forming part of a fuel tank of an aircraft. The valve is itself controlled by means of an actuator. For safety reasons, the actuator, which is electrically powered, is located outside the tank, while the valve is inside it. These two members are thus positioned on opposite sides of the panel of the tank, being pressed against respective opposite faces of the panel. This assembly is provided by sandwiching the panel between the valve and its actuator. The valve is controlled with the help of a fluted shaft that forms part of the valve or of the actuator and that engages in a likewise-fluted bore in the other one of said members. It is thus important for the points on the panel against which these two members bear to be accurately parallel in order to guarantee that the shaft and its bore share a common axis.
The assembly of the valve and the actuator is subjected to dimensional tolerances, amongst which the thickness of the panel is thus a major item, as is the relative alignment of the valve with its actuator, where this alignment is often associated with the parallelism of the two faces of the panel. The quality with which the valve and the actuator are assembled together is thus associated with the quality of the panel itself, and in particular with the parallelism of its two bearing faces and on the tolerances concerning its thickness.
In addition, if the panel is made not of metal but of composite material, then additional defects may arise that have an influence on parallelism and on tolerance. The thickness of a panel made of composite material depends in particular on its baking and on the matrix making it up. Baking causes the composite material to expand, thereby causing the thickness of the panel to vary, so its thickness needs to be inspected closely. Furthermore, for large structural panels made of composite material, it is difficult to ensure that both bearing faces are accurately parallel. This expansion and lack of parallelism can give rise to problems when assembling items of equipment such as the valve together with its actuator.
Various solutions exist for mitigating that problem. Thus, finishing machining may be performed directly on the panel in order to obtain the design assembly tolerances. However that involves an additional operation that is relatively lengthy. It is also possible to add metal spacers on either side of the panel, which spacers are adjusted prior to assembling the valve and the actuator and act as an interface between those members and the faces of the panel against which they bear. Nevertheless, those constitute additional parts that increase the volume and the weight of the assembly as a whole.